http://www.beckmancoulter.com/resourcecent...s/rotorcalc.asp

Nice, do they have it for eppendorf centrifuges?

The relationship between revolutions per minute (RPM) and relative centrifugal force (xg) is:
g = (1.118 × 10^-5) R S²
where g is the relative centrifugal force, R is the radius of the rotor in centimeters, and S is the speed of the centrifuge in
revolutions per minute.

You can use this for any centrifuge, just measure the radius of the rotor from the center to outer edge.

You can use this one for all centrifuges too, if you're lazy. Even with a Nomogram for it.